Despite the recent breakthroughs of polymer solar cells (PSCs) exhibiting a power conversion efficiency of over 17%, toxic and hazardous organic solvents such as chloroform and chlorobenzene are still commonly used in their fabrication, which impedes the practical application of PSCs. Thus, the development of eco-friendly processing methods suitable for industrial-scale production is now considered an imperative research focus. This Review provides a roadmap for the design of efficient photoactive materials that are compatible with non-halogenated green solvents (e.g., xylenes, toluene, and tetrahydrofuran). We summarize the recent development of green processing solvents and the processing methods to match with the efficient photoactive materials used in non-fullerene solar cells. We further review progress in the use of more eco-friendly solvents (i.e., water or alcohol) for achieving truly sustainable and ecofriendly PSC fabrication. For example, the concept of water-or alcohol-dispersed nanoparticles made of conjugated materials is introduced. Also, recent important progress and strategies to develop water/alcohol-soluble photoactive materials that completely eliminate the use of conventional toxic solvents are discussed. Finally, we provide our perspectives on the challenges facing the current green processing methods and materials, such as large-area coating techniques and long-term stability. We believe this Review will inform the development of PSCs that are truly clean and renewable energy sources.

BackgroundHybridization is an important evolutionary process that results in increased plant diversity. Flowering Prunus includes popular cherry species that are appreciated worldwide for their flowers. The ornamental characteristics were acquired both naturally and through artificially hybridizing species with heterozygous genomes. Therefore, the genome of hybrid flowering Prunus presents important challenges both in plant genomics and evolutionary biology.ResultsWe use long reads to sequence and analyze the highly heterozygous genome of wild Prunus yedoensis. The genome assembly covers > 93% of the gene space; annotation identified 41,294 protein-coding genes. Comparative analysis of the genome with 16 accessions of six related taxa shows that 41% of the genes were assigned into the maternal or paternal state. This indicates that wild P. yedoensis is an F1 hybrid originating from a cross between maternal P. pendula f. ascendens and paternal P. jamasakura, and it can be clearly distinguished from its confusing taxon, Yoshino cherry. A focused analysis of the S-locus haplotypes of closely related taxa distributed in a sympatric natural habitat suggests that reduced restriction of inter-specific hybridization due to strong gametophytic self-incompatibility is likely to promote complex hybridization of wild Prunus species and the development of a hybrid swarm.ConclusionsWe report the draft genome assembly of a natural hybrid Prunus species using long-read sequencing and sequence phasing. Based on a comprehensive comparative genome analysis with related taxa, it appears that cross-species hybridization in sympatric habitats is an ongoing process that facilitates the diversification of flowering Prunus.Electronic supplementary materialThe online version of this article (10.1186/s13059-018-1497-y) contains supplementary material, which is available to authorized users.

Isoetes is a widely distributed lycophyte genus of at least 200 species occurring in diverse habitats. The species can be difficult to identify because Isoetes, with its apparent simplicity of form and conserved morphology, provides few diagnostic features to reliably distinguish its species. The last worldwide monograph, published nearly a century ago, listed 77 taxa. The first step in producing a flora or monograph of all known species of a genus is to compile a list of the acceptable species names. The list presented here is a compilation of 192 accepted names representing taxa from regions around the world: chromosome numbers were assigned to 101 of them, with polyploidy settled on 46.7%. Distribution mapping of the accepted species indicates that South America is the center of diversity for Isoetes and species diversity is the highest in temperate regions. Many of the species on this list are rare and have limited ranges. The list of taxa can be used to initiate floristic studies and conservation efforts in keeping with the target goals of the Global Strategy for Plant Conservation.

Despite considerable progress, many details regarding the evolution of the Arcto-Tertiary flora, including the timing, direction, and relative importance of migration routes in the evolution of woody and herbaceous taxa of the Northern Hemisphere, remain poorly understood. Meehania (Lamiaceae) comprises seven species and five subspecies of annual or perennial herbs, and is one of the few Lamiaceae genera known to have an exclusively disjunct distribution between eastern Asia and eastern North America. We analyzed the phylogeny and biogeographical history of Meehania to explore how the Arcto-Tertiary biogeographic hypothesis and two possible migration routes explain the disjunct distribution of Northern Hemisphere herbaceous plants. Parsimony and Bayesian inference were used for phylogenetic analyses based on five plastid sequences (rbcL, rps16, rpl32-trnH, psbA-trnH, and trnL-F) and two nuclear (ITS and ETS) gene regions. Divergence times and biogeographic inferences were performed using Bayesian methods as implemented in BEAST and S-DIVA, respectively. Analyses including 11 of the 12 known Meehania taxa revealed incongruence between the chloroplast and nuclear trees, particularly in the positions of Glechoma and Meehania cordata, possibly indicating allopolyploidy with chloroplast capture in the late Miocene. Based on nrDNA, Meehania is monophyletic, and the North American species M. cordata is sister to a clade containing the eastern Asian species. The divergence time between the North American M. cordata and the eastern Asian species occurred about 9.81 Mya according to the Bayesian relaxed clock methods applied to the combined nuclear data. Biogeographic analyses suggest a primary role of the Arcto-Tertiary flora in the study taxa distribution, with a northeast Asian origin of Meehania. Our results suggest an Arcto-Tertiary origin of Meehania, with its present distribution most probably being a result of vicariance and southward migrations of populations during climatic oscillations in the middle Miocene with subsequent migration into eastern North America via the Bering land bridge in the late Miocene.

This study examines phylogenetic relationships among the 12 genera of Urticeae (Urticaceae) and investigates the pattern of morphological evolution based on analysis of nuclear ribosomal internal transcribed spacer (nrITS) and two plastid DNA regions (rbcL exon, trnL-F spacer). Sequence data were analyzed using maximum parsimony and Bayesian inference, and selected morphological traits were mapped onto the molecular tree. The molecular results strongly supported monophyly of Urticeae, excluding Gyrotaenia, which is related to Elatostemateae. All genera were monophyletic except for Urtica, Laportea, and Urera. Two Hesperocnide species are nested within Urtica. Laportea and Urera are divided into three groups with a strong geographical signal. The inferred phylogeny indicates five well-supported clades in Urticeae: clade A including Urtica (with Hesperocnide), Zhengyia, Laportea I, and Nanocnide; clade B comprising Dendrocnide and Discocnide; clade C including only Girardinia; clade D including Laportea II; and clade E including Obetia, Urera I, II, III, and Poikilospermum. Although it is difficult to identify morphological synapomorphies for these well-defined clades within Urticeae, character analysis shows that the herbaceous habit and alternate leaves are the ancestral states in the tribe. The presence of stinging hairs is the derived status in Urticeae, and it might have been a key innovation triggering species diversification in the tribe.

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We present a new series of fullerene derivatives that exhibit solubility in ethanol/water solvent mixtures and implement these materials to fabricate polymer solar cells (PSCs) using environmentally benign solvents. In order to simultaneously optimize the processability of the fullerenes in ethanol/water solvent mixtures and device performance, different fullerene mono-adducts were designed by introducing oligoethylene glycol side chains with different lengths and number of branches. As a result, we achieved power conversion efficiencies up to 1.4% for PSCs processed from benign ethanol/water mixtures in air. Significantly, the new alcohol/water-soluble fullerene derivatives displayed electron mobilities up to 1.30 × 10 −4 cm 2 V −1 s −1 , 150 times higher than those of a previously reported alcohol-soluble fullerene bis-adduct, owing to efficient packing of the fullerenes. Femtosecond transient absorption spectroscopy revealed the acceptor side chain to markedly impact geminate and/or nongeminate charge recombination in the PSCs. In addition, side chain optimization of these fullerenes produced well-intermixed morphologies with high domain purity when blended with p-type polymer to provide hole and electron transport pathways. Our results provide important guidelines for the design of electroactive materials for safe and environmentally benign fabrication of PSCs and other organic electronic devices.

Polyploidy plays an important role in the speciation of Isoëtes. Increasing our knowledge about the specific origin of each polyploid or phylogenetic relationship among species has been hampered because of conserved morphological variation and scarce habitats. We present several hypotheses concerning the speciation pathways of Isoëtes species distributed in East Asia. Our hypotheses are inferred from phylogenetic relationships that were elucidated using sequences of the internal transcribed spacer regions of nuclear ribosomal DNA, a second intron of LEAFY, and chloroplast DNA trnS-psbC spacer regions. These inferred phylogenetic relationships indicated that (1) the Chinese tetraploid, I. sinensis, is closely related to I. yunguiensis; (2) the Korean endemic species, I. hallasanensis, is an autotetraploid derived from I. taiwanensis or closely related taxa; (3) the hexaploid I. coreana forms a clade and has its closest evolutionary relationships with I. taiwanensis or I. hallasanensis; and (4) the Japanese hexaploid I. japonica is closely related to I. taiwanensis-I. coreana and I. sinensis-I. yunguiensis. These results suggest that interspecific hybridization and polyploidization have played central roles in speciation of East Asian Isoëtes. Furthermore, I. taiwanensis, an endemic species in Taiwan, has been involved in at least three cases of autopolyploid or allopolyploid speciation in East Asia.